System and method for measuring the magnetic conductive properties of a test fluid

Abstract

The magnetic or conductive properties of a test fluid, or of particles within a test fluid, are measured by an apparatus comprising a solenoidal coil (1a), a magnetic field carrying means (23) disposed radially outside the solenoidal coil, a tubular electrostatic screen (22) disposed radially within the solenoidal coil and radially outside a sample detecting volume, the test fluid being disposed in use within the sample detecting volume and separated radially from the innermost surface of the electrostatic screen by an air gap (18). The solenoidal coil is energised in use, and sensing means is provided for sensing the impedance of the solenoidal coil.

I claim: 
     
       1. Apparatus for measuring the magnetic or conductive properties of a test fluid, the apparatus comprising a solenoidal coil defining an interior space including a sample detecting volume, a magnetic field carrying means disposed radially outside the solenoidal coil, a tubular electrostatic screen disposed radially within the interior space defined by the solenoidal coil and radially outside the sample detecting volume such that test fluid can be disposed within the sample detecting volume and be separated radially from the innermost surface of the electrostatic screen by a gap, energizing means for energizing the solenoidal coil, and sensing means for sensing the impedance of the solenoidal coil. 
     
     
       2. Apparatus as claimed in claim 1 in which the solenoidal coil is wound around the radially outer surface of a bobbin and the electrostatic screen is positioned on the radially inner surface of the bobbin, the screen being adapted to be earthed in use. 
     
     
       3. Apparatus as claimed in claim 2 in which the field carrying means is arranged to support the coil. 
     
     
       4. Apparatus as claimed in claim 3 in which opposite ends of the coil bobbin are attached to the innermost radial surface of the field carrying means. 
     
     
       5. Apparatus as claimed in claim 3 in which the magnetic field carrying means is of tubular shape, and in which the bobbin of the solenoidal coil is fixed to the tubular magnetic field carrying means by means of a resilient compound. 
     
     
       6. Apparatus as claimed in claim 5 in which the resilient compound is a silicone rubber. 
     
     
       7. Apparatus as claimed in claim 1 in which the magnetic carrying means is constructed substantially of a ferrite material. 
     
     
       8. Apparatus as claimed in claim 1 in which the tubular screen extends axially beyond both ends of the coil. 
     
     
       9. Apparatus as claimed in claim 1 in which the magnetic field carrying means extends axially beyond both ends of the coil. 
     
     
       10. Apparatus as claimed in claim 1 in which the magnetic field carrying means is of tubular shape. 
     
     
       11. Apparatus as claimed in claim 1 in which the coil is a single-layer coil. 
     
     
       12. Apparatus as claimed in claim 1 provided with a non-conductive sample location tube coaxially disposed with respect to the coil, the arrangement being such that, in use, the outermost radial surface of the non-conductive sample location tube is separated from the innermost radial surface of the screen by the gap. 
     
     
       13. Apparatus as claimed in claim 1 further comprising a tubular outer metallic shield that surrounds the exterior of the solenoidal coil for providing a barrier to external electromagnetic interference such that the external interference is substantially prevented from entering the detecting volume by the metallic shield. 
     
     
       14. Apparatus as claimed in claim 1 wherein the detecting volume is further defined by a tubular container disposed within the interior space defined by the solenoidal coil. 
     
     
       15. Apparatus as claimed in claim 1 in which said gap contains air. 
     
     
       16. A method of measuring the magnetic or conductive property of a test fluid in a testing apparatus comprising a solenoidal coil defining an interior space including a sample detecting volume, a magnetic field carrying means disposed radially outside the solenoidal coil, a tubular electrostatic screen disposed radially within the interior space defined by the solenoidal coil and radially outside the sample detecting volume, energizing means for energizing the solenoidal coil, and sensing means for sensing the impedance of the solenoidal coil, the method comprising the steps of: disposing the test fluid within the sample detecting volume such that the test fluid is separated radially from the innermost surface of the electrostatic screen by a gap;   energizing the solenoidal coil; and   sensing the impedance of the solenoidal coil to determine the magnetic or conductive properties of the test fluid.   
     
     
       17. A method as claimed in claim 16 in which the fluid is a powder. 
     
     
       18. A method as claimed in claim 16 in which the fluid is a liquid containing a powder.